This invention relates generally to an electronic hygrometer and an electronic thermometer-hygrometer (hereinafter referred to as "electronic thermohygrometer"). More specifically, the invention relates to a digital electronic hygrometer including a humidity sensor which detects the change in humidity of the atmosphere and produces an electric signal corresponding to the detected humidity change, and relates also to a digital electronic thermohygrometer including, in addition to the humidity sensor, a temperature sensor whose electric resistance or electrostatic capacity is variable with the temperature change of the atmosphere.
As is well known, digital electronic hygrometers of this type are comprised of a sensor unit including a humidity sensor which detects the humidity change of the atmosphere and produces an electric signal corresponding to the detected humidity change; and a signal processing unit connected to the sensor unit and consisting essentially of an amplifier, analog-to-digital converter (hereinafter referred to as "a-d converter"), and digital electronic circuit controls such as a microcomputer and microprocessor (the controls being hereinafter referred to as "microcomputer"). In the digital electronic hygrometer, an analog voltage signal produced by and output from the humidity sensor of the sensor unit is input to the signal processing unit, where the signal is amplified by the amplifier and is converted into a digital signal through the a-d converter. The digital signal is then led to the microcomputer which calculates the humidity value of the atmosphere on the basis of the digital signal.
As is obvious from the foregoing, the conventional digital electronic hygrometer requires that the amplifier for amplifying an analog signal output from the humidity sensor and the a-c converter for converting the analog signal from the amplifier into a digital one be connected in between the humidity sensor and the microcomputer, so that the microcomputer can calculate the humidity of the atmosphere on the basis of the analog voltage signal produced by the humidity sensor correspondingly to the atmospheric humidity change. The requirement has made it difficult to contain the whole circuitry inclusive of the microcomputer, amplifier, a-d converter, and the like in a single LSI chip, with consequent limitations on miniaturization, power saving, and cost reduction.
In view of these, we have made an extensive study and have found that the number of circuit components of the digital electronic hygrometer can be reduced and the whole circuitry built up as a single-chip LSI by omitting the relatively expensive a-d converter and using instead other technical means having the function of the converter.
It has also been found possible to build, in a single-chip LSI, the electronic thermohygrometer that can measure both the humidity and temperature by incorporating a thermistor or other element as a temperature sensor in the circuit of the digital electronic hygrometer.
The present invention is based upon these novel discoveries.